Regenerator for syngas cleanup and energy recovery in gasifier systems

ABSTRACT

A rotating heat regenerator is used to recover heat from the syngas at it exits the reactor vessel of a waste or biomass gasifier. In some embodiments, three or more streams are passed through the heat exchanger. One stream is the dirty syngas, which heats the rotating material. A second stream is a cold stream that is heated as it passes through the material. A third stream is a cleaning stream, which serves to remove particulates that are collected on the rotating material as the dirty syngas passes through it. This apparatus can also be used as an auto-heat exchanger, or it can exchange heat between separate flows in the gasifier process. The apparatus can also be used to reduce the heating requirement for the thermal residence chamber (TRC) used downstream from the gasification system.

This application claims priority of U.S. Provisional Patent Application61/181,099, filed May 26, 2009, the disclosure of which is incorporatedherein by reference.

BACKGROUND

The generation of waste, particularly solid waste has become anincreasingly worrisome environmental issue. Many landfills are becomingfilled to the point where additional waste cannot be deposited therein.In addition, much of today's solid waste is not readily biodegradable,implying that the waste will not decompose in a timely manner. As analternative, incinerators have been employed to burn solid waste, so asto minimize its physical footprint. However, these incinerators burn thewaste and generate air pollutants which require very extensive gascleanup, create ash which can be hazardous and produce energy only inthe form of heat which is converted into electricity.

Plasma gasifiers offer an alternative to these current approaches.Plasma gasifiers use intense electrically based heating to enhance agasification and melting process which produces a synthesis gas (syngas)consisting of hydrogen and carbon monoxide. Inorganic material isconverted into a nonleachable glass. After cleaning, the synthesis gascan be converted into a variety of liquid fuels or combusted to produceelectricity. Cleaning of the synthesis gas and recovering heat from thesyngas can be a key part of the process.

FIG. 1 shows a representative plasma gasifier system. The plasmagasifier system 100 includes a reactor vessel 110, which is typicallyrefractory lined. Within the vessel 110 are two or more electrodes 120a, 120 b that are in electrical communication with one or more powersupplies 130. In some embodiments, one electrode is suspended from thetop of the reactor vessel 110, while the other electrode 120 b islocated at the bottom of the vessel. The power supplies 130 create asignificant electrical potential difference between the two or moreelectrodes, so as to create an arc between the electrodes 120 a, 120 b.As waste is fed into the vessel 110 via a waste handler 140, it isexposed to extreme temperatures, which serve to separate the waste intoits component parts.

The bottom, or lower portion of the vessel 110 contains molten metal145. An area above the molten material forms an inorganic slag layer147. Gasses, such as carbon monoxide and hydrogen gas, are separated andexit the vessel though portal 150. The gas, commonly known as syngas,exits the vessel 110 at an excessive temperature. Since the gas has notbeen processed, it is also referred to as dirty syngas. The syngas iscooled in a scrubber unit 180 to allow other particulates in the gas,such as carbon or sulfur to precipitate out of the gas. Halogens andacidic materials are also removed from the syngas. The resulting gas isnow referred to as clean syngas. The clean syngas can then be used tofuel a boiler or other device.

Despite the advantages of plasma gasifiers, one issue associated withthe use of plasma gasifiers is the amount of energy used to raise thetemperature of feedstocks, the syngas and the slag. This heat is thenlost when the syngas is cooled as it is being cleaned. Recovery of thiswould increase the economic benefits of plasma gasifiers.

Therefore, in some embodiments, a regenerator or heat exchanger 160 maybe used to capture the heat from the dirty syngas as it exits the vessel110 and transfer it to another medium 170, such as to water to createsteam. Heat recovery can also be used for a range of applications in thegasification train, including reducing the heating requirements forfinal stage removal of tars and other undesirable compounds and for usein powering a turbine. Such a turbine can be used for a variety ofapplications, including electricity production, and powering pumps,blowers, or compressors for separation of oxygen from air. Althoughstationary regenerators with extensive valving may be used, it may beadvantageous to utilize a moving structure, such as a ceramic structure,due to the high temperatures involved in the process.

However, the use of heat exchangers (also known as regenerators) inwaste and biomass gasification systems has been inhibited by the harshenvironment in which they must operate. First, the syngas, at the pointit passes through the heat exchanger, is not clean. In other words, itstill contains particulates and condensables, such as tars and otherimpurities that can be captured and clog the heat exchanger. Once tarsand other particulates collect on the heat exchanger, the flow of gasthrough the exchanger is compromised, thereby impacting the utility ofthe device. The honeycomb structures which have been considered forrecuperation in other applications do not have sufficiently smallmicrohole structures to capture the particulate matter. In addition, thesyngas at this point is at extremely high temperatures, making theselection of a suitable material for a heat exchanger difficult.

In addition, many heat exchangers/regenerators operate by reversing the“hot” and “cold” streams to effectively transfer the heat collected bythe exchanger. This often means that the heat exchanger media has tomove or rotate to affect this reversal of streams. Movement and sealingof moving parts at high temperatures is often problematic.

Therefore, there is a need for an effective apparatus and method toutilize the heat generated within a plasma gasifier. The apparatus mustnot only exchange heat, but also tolerate and remove particulate buildupon its surface, while operating at extreme temperatures.

SUMMARY OF THE INVENTION

The problems of the prior art are overcome by the apparatus and methoddisclosed herein. A rotating or otherwise moving material is used torecover heat from the syngas at it exits the reactor vessel. In someembodiments, three or more streams are passed through the heatexchanger. One stream is the dirty syngas, which heats the rotatingmaterial. A second stream is a cold stream which is heated as it passesthrough the material. A third stream is a cleaning stream, which servesto remove particulates and other deposits that condense on theregenerator material that are collected on the rotating material as thedirty syngas passes through it. This apparatus can also be used as anauto-regenerator (that is, the same material flows through the hot andthen cold section of the regenerator), or it can exchange heat betweenseparate flows in the gasifier process. The apparatus can also be usedto reduce the heating requirement for the thermal residence chamber(TRC) used downstream from the gasification system, and thereby reducethe amount of syngas that must be oxidized and the amount of oxygen thatmust be provides in order to heat the TRC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plasma gasifier system which can be used with the presentinvention;

FIG. 2A shows a rotating heat exchanger;

FIG. 2B shows a cross-sectional view of a rotating heat exchanger;

FIG. 3A shows one embodiment using a rotating heat regenerator;

FIG. 3B shows a second embodiment using a rotating heat regenerator;

FIG. 3C shows an embodiment using multiple rotating heat regenerators;

FIG. 4 shows a cross sectional view of a rotating heat regeneratoraccording to one embodiment;

FIG. 5 shows a cross sectional view of a rotating heat regeneratoraccording to a second embodiment;

FIG. 6 shows a cross sectional view of a rotating heat regeneratoraccording to a third embodiment;

FIGS. 7A-B shows a first embodiment of a seal that can be used with therotating heat regenerator;

FIG. 8 shows a second embodiment of a seal that can be used with therotating heat regenerator; and

FIG. 9 shows an embodiment using a non-monolithic heat regenerator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2A shows a schematic diagram of a rotating energy exchanger 200.The energy exchanger 200 may be located between the vessel 110 and otherdownstream components 220. FIG. 2B shows a representative crosssectional view of an energy exchanger 300. The heated stream passesthrough a portion 310 of the energy exchanger, while a cold stream ispassed through a second portion 320. The line 315 between the twoportions signifies a wall or other separator that keeps the two flowsapart. The heated stream imparts its thermal energy to the first portion310 of the energy exchanger 300. The energy exchanger 300 is rotated,such that the recently heated portion of the energy exchanger 300 is notused by the heated stream. Instead, the cold stream flows through theheated portion of the energy exchanger, where the energy flows from thethermal mass of the energy exchanger 300 to the cold stream. The neteffect is that the heated portion 310 releases its stored heat to thecold stream. Although rotating heat exchangers have been used for heatrecovery from clean gas, they have not been used with syngas as it exitsa gasifier, where it still contains contaminants and condensables, suchas tars and alkalis, or used in an auto-heat exchanger, where the samegas moves through both legs of the energy exchanger. An advantage ofrotating energy exchangers is that they do not require valving of theinlet and output of the various legs of the energy exchanger, allowingoperation at higher pressures and temperatures. However, this is notintended to limit the invention to only this type of moving energyexchanger.

In some gasifier applications, there is little pressure differentialbetween the multiple flows through the regenerator, thereby minimizingleakage.

In one embodiment, shown in FIG. 3A, the present invention includes anauto-heat exchanger, where the same gas flows through the separateportions of the exchanger 300. For example, the outlet of the gasifiervessel 110 is fed into a first portion 310 of the material and iscooled. After it is cooled, the raw syngas passes through a first flowpath 311 and processed by downstream components 220, as described below.The cleaned syngas exits the downstream components 220, and passesthrough a second flow path 312 and then flows through a second portion320 of the material, thereby getting heated so as to reach a temperatureclose to that at which it exited the gasifier 110. In this embodiment,the exchanger 300 may have deposits of tar and slag. The downstreamcomponents 220 remove the rest of the particulates, condensables orother undesirable material from the syngas, before it is sent back tothe exchanger to be heated. In some embodiments, a cooling elementwithin the downstream components 220 is used to provide a region that iscooled or refrigerated to allow the condensation and precipitation ofcontaminants from the syngas.

FIG. 3B shows a second embodiment of a gasifier using the present heatexchanger. In this embodiment, the raw syngas is used to heat the firstportion 310 of the heat exchanger 300, as described above. However,rather than sending the clean syngas through the second portion 320 ofthe heat exchanger 300, a different fluid is used. In some embodiments,the fluid being heated is used to operate a turbine.

In some embodiments, the best thermal performance of the energyexchanger is when the cold fluid flows in the direction opposite fromthe hot fluid, in order to minimize entropy generation and achieve bestthermal recovery efficient.

Honeycomb structures may be used to create the energy exchangers. It isalso possible to use monolith structures, similar to those used indiesel particulate filters (DPF). In the case of DPFs, the syngas flowsthrough small pores present in the wall, such that the gas has to flowthrough a wall, thereby depositing solids upstream from the walls, as isdone in conventional DPF filters for automotive applications. In thecase of a honeycomb, the tars and/or slag condense in the channels andthen precipitate on the walls of the honeycomb.

The energy exchanger 300 can be made from a variety of materials. Insome embodiments, cordierite is used. However, there is a temperaturelimitation of about 1300° C., as indicated in Table 1. The actualtemperature limitation may be much lower than this, such as about 700°C., if the material is cycled multiple times. Another attractivematerial is SiC. This material has a higher maximum temperature andreduced cycling limitations. One drawback of SiC is that it has highthermal conductivity, and thus there is substantial heat transfer alongthe regenerator, thereby decreasing its efficiency. This limitation isnot present if the SiC is discretized in the axial direction, as wouldbe the case when the energy exchanging material is in the form ofpellets, having spherical or other shapes. In this case, the highthermal conductivity of the energy exchanging media would be beneficial,as there will small temperature gradients across the energy exchangingmaterial, better using the thermal capacity of the pellets. For gasifierapplications, optimal efficiency may not be the most criticalcharacteristic, as there may be other criteria, in particularoperational constraints, which drive the operation of these units. Insome embodiments, a metallic heat exchanger can be used, however theiruse may be limited by the reducing nature of the environment.

TABLE 1 Material Characteristics for Energy Exchanger Ceramic OxideCarbide Metal PROPERTY (e.g. Cordeirite) (e.g. SiC) (e.g. HJS, SMF)Strength A-axis A-axis Tensile Crush 7.93 MPa Crush 9.65 MPa 40 MPax-axis 60 MPa y-axis Heat 2.8 3.6 4.2 Capacity (@500° C. J/cm³C) Thermal1-2 10-30 ~15 Conductivity (@500° C. W/mK) CTE <6 45 180 (×10⁻⁷/° C.,22-10000° C.) Elastic 4.8 GPa 13.3 GPa elongation at Modulus break: 40%x-axis 20% y-axis Maximum ~1300° C. ~1600° C. ~1360° C. temperature

The thermal mass in the energy exchanger can be a monolith (such as ahoneycomb monolith, with or without plugs in alternative channels, as indiesel particulate filters (DPFs)), or it can be a discretized material,such as pellets. As mentioned above, discretized materials have loweraxial thermal conduction; axial heat conduction results in decreasedperformance of the energy exchanger 300. It is important to produceenough surface area, level of turbulence and heat capacity in order toremove the desired energy from the flow. In the case of pellets, theycan be relatively uniform sized, or they can be of different sizes inorder to increase the filling fraction or the heat transfer from the gasto the solid phases.

In order to assure a thermal gradient along the energy exchangingmaterial in the case of the auto-energy exchanger, a thermal sink needsto be placed in the region between the heated stream and the coldstream, such as in a cooling element of the downstream components 220 inFIG. 3A. In the case of the auto-energy exchanger, this is the regionwhere the flows change direction. The cooling element of the downstreamcomponents 220 in FIG. 3A is the coldest region of the energy exchanger.By minimizing heat leaks along the energy exchanger and leakages betweenthe inlet and the outlet legs of the energy exchanger, the refrigerationthat needs to be provided to the cooling element in downstreamcomponents 220 can be minimized. The temperature in this region will bedetermined by the efficiency of heat removal from the gas to the solidmaterial, the flow rate, the leakage between the two flows, and therefrigeration power in the cooling element 220.

In another embodiment, the reverse process, where the hot gas is furtherheated instead of cooled, can also be used. If, instead of refrigerationin downstream component 220, heat is added, the function of the heatexchanger 300 reverses. That is, the hot stream (i.e. the raw or dirtysyngas) gets hotter in the first leg of the energy exchanger, while inthe return leg the stream (clean gas) gets cooler. As in the case of thepreviously described embodiment, the temperature at the hot zone(depicted by 220 in FIG. 3A) depends on the leakage, on the thermalconduction, on the heat transfer between the streams and the thermalmass that constitutes the energy exchanger, etc. Instead of depositingthe condensable materials, high temperatures can be reached in thisconfiguration to complete reactions that are slow at lower temperature,including conversion of medium and heavy hydrocarbons to hydrogen richgas and CO. The process can be used to remove some of the contaminants(such as tars and remaining medium and light hydrocarbons), butcontaminants like ash and other slag-forming materials (such as sodium)will not be removed from the stream. The temperatures are such that thetars are pyrolyzed or reformed, with or without oxygen. The clean syngasenters the second leg of the heat exchanger, where it is cooled by theincoming dirty syngas and exits the heat exchanger at a temperaturecomparable to that at which it enters. Thus it is possible to increasethe temperature of the syngas to that required for destruction of thetars with a relatively small energy penalty.

In this case, the heating of the hottest zone can be provided throughelectrical heating, thermal heating, combustion of a fuel (external tothe device) or other means. In particular, microwave heating of thissection can be an attractive possibility, with antennas/waveguideprotected behind a ceramic liner.

The material characteristics of the regenerator can be adjusted to matchthe local requirements of the regeneration as a function of the locationof the heat exchanger 300. Thus, different materials can be used at theregion of high temperature rather than lower temperatures, minimizingthe cost of the expensive material and increasing the range of materialsthat can be used. Alternatively or in conjunction with the use ofmultiple materials, the specific surface (surface area per unit volume)of the regenerator can be altered, with comparable fill fractions, tomatch changes in physical or chemical characteristics of the flow. Thiscan be achieved by changing the size of pellets, if pellets are used asthe material in the regenerator. It is also possible to change the fillfraction, for example, by adjusting the pellet size distribution (usingpolydispersive pellets, for example). It is not necessary to depend onthe use of pellets, as other methods can be used to adjust the specificsurface. It is also possible to vary the porosity of the material as afunction of the location along the heat exchanger.

In the case when the rotating element of the heat exchanger is notmonolithic, it would be possible for the gas to mix through the heatexchanger, decreasing the efficiency of the system. To prevent excessivemixing, the moving section of the energy exchanger 900 is made inseveral compartments 980, as indicated in FIG. 9. The energy exchanger900 has a plurality of these compartments 980, and both the dirty syngasas well as the cleaned syngas flow through multiple compartments. Thecompartments 980 have walls 950 along the radius that prevent gas flowin the poloidal direction (which would “short-circuit” the exchanger900) thus preventing mixing between gas introduced in one compartmentfrom mixing with gas in an adjacent compartment. Pellets, or discreteheat-exchanging material 960 fill each of the compartments 980. Mixingfrom one compartment to another can be prevented by using stationaryseals 940, 930 at the top and/or bottom of the rotating heat exchanger,respectively. As shown in FIG. 9, if the poloidal extent θ_(s) of thetop stationary seal 940 or bottom stationary seal 930 is larger than thepoloidal extent θ_(s) of the compartment 980, then leakage flow throughone compartment 980 can be eliminated. Furthermore, there is always asealing region 970 present, eliminating the short-circuit route betweencompartments.

It is also possible to utilize multiple regenerators 300 a, 300 b inseries, as shown in FIG. 3C. In this embodiment, raw syngas exits afirst portion of exchanger 300 a, and passes through first flow path311. It then enters a first portion of second exchanger 300 b. The gasexiting the second exchanger 300 b passes through another flow path 313to downstream components 220. Gas exiting the downstream components 220then passes through another flow path 314 to a second portion of secondexchanger 300 b. Gas exiting the second exchanger 300 b passes throughsecond flow path 312 and enters a second portion of first exchanger 300a. In one embodiment, the exchangers 300 a, 300 b may use differentmaterials, depending on the thermal requirements andparticulate/condensable content of the syngas. The discrete nature ofthe heat exchanger shown in FIG. 3C allows for distributed conditioningof the regenerators 300 a, 300 b. For example, regenerator 300 a mayneed to be regenerated more frequently than regenerator 300 b due to itsexposure to raw or dirty syngas. Similarly, the technique used toregenerate each regenerator 300 a, 300 b may be different (i.e. one mayuse heat while the other uses an oxidizer). In some embodiments, theportion of each regenerator 300 a, 300 b that is subjected toregeneration may differ. Methods of regenerating the surfaces of theheat exchangers 300 are described in more detail below.

As shown in FIG. 3C, an additional element 221 may be located betweenrotating regenerators 300 a, 300 b, such as in flow path 312. Thiselement 221 can be used to introduce conditioning material to a sectionof the regenerator 300 a, or to remove conditioning material from theregenerator 300 b. This component can also be used as a heat sink or aheat source, if desired. In some embodiments, multiple middle streamcomponents 221 can exist. For example, middle stream components 221 maybe placed in both flow streams 311, 312. Similarly, more than tworotating regenerators can be present. In some embodiments, theregenerators 300 a, 300 b may be placed in series without middle streamcomponents 221 between them. It is also possible to divert a section ofthe main flow, such as from flow path 311 or flow path 312, if flows atintermediate temperatures are desired.

In some embodiments, the use of DPF-like structures may bedisadvantageous because the velocities of the flows through the systemare higher, as only a portion of the available cross section is used ineach phase of operation. This is due to the fact that a portion of thechannels in the matrix are sealed on one side of the regenerator, whileadjacent channels are sealed on the opposite side. This results innon-uniform velocities through the channels; however, the geometryprovides for good thermal contact between the gas and the thermal masswhile flowing in the microstructures (pores) through the walls betweenadjacent channels since all gas must flow through the walls.

In the case of DPF-like geometry for the energy exchanger, it ispossible to arrange the channels in the regenerator such that they areshaped to allow more uniform flows through the channels. Thus, the crosssection of a channel decreases along the channel, moving away from theopening of the channel. Another option is to make the channelcross-sections different for the set of channels with openings on oneside of the regenerator. There may be advantages with these geometriesdepending on the loading of the regenerator by solids/slags/slurries.The objective may be to arrange the asymmetric matrix such that the tarsand other solids are deposited on channels with larger cross sections.

It is known that, in some embodiments, gas exiting a gasifier must becooled in order to remove (through condensation) tars and/or slags. In aregion further downstream, the gas may be further cooled to precipitateany remaining tars/slags that were not removed earlier. Referring toFIG. 1, it would be preferable if tars were deposited on the coolersections of the heat exchanger 160, while the slags, such as alkalimetals, were condensed/deposited downstream on a separate surface 180.

The use of two flows through a ceramic honeycomb structure, as shown inFIG. 2B, has been disclosed previously. However, there are substantialadvantages, such as for gasifier applications, of utilizing more thantwo flows.

In some embodiments, as shown in FIG. 4, a third flow, referred to as HXcleaner fluid, may be used. This exchanger 400 utilizes three portions410, 420, 430. As described with respect to FIG. 2B, hot dirty syngaspasses through the first portion 410 and is cooled as it passes throughthe exchanger 400. A cool stream (either clean syngas, turbine fluid, oranother fluid) passes through second portion 420 and is heated by theexchanger 400. The third flow is introduced to clean a portion 430 ofthe heat exchanger 400. Lines 415 signify walls or other separators inthe stationary sections designed to keep the flows separate from oneanother. In some embodiments, this third flow may involve an oxidizer,such as oxygen or air. At high temperatures, the oxidizer may increasethe combustion rates of the tars on the heat exchanger. In otherembodiments, the HX cleaner fluid is not an oxidizer and the flow ofhigh temperature gas to enable the evaporation of the slags on theexchanger. In other embodiments, high flow rates are used to removeparticulates deposited on the exchanger. This embodiment may beparticularly useful when DPF-like geometry is used for heat (energy)exchanger. Thus, the heat exchanger (HX) cleaner is used to remove theparticulates and condensables, such as tar, that are deposited on theexchanger, either via combustion or evaporation.

The flow direction of the HX cleaner fluid may be the same as that ofthe syngas exiting the gasifier. In other embodiments, the flow of HXcleaner fluid may be opposite than of the syngas exiting the gasifier.It is also possible to mix the output from the HX cleaner section witheither the dirty syngas, or the cleaned gas. If mixed with clean gas,this can happen at any point along the gasification process. In otherembodiments, it is not necessary to return the flow from the HX cleanerportion to the syngas. For example, if slags are deposited on the heatexchanger, or tars are simply re-evaporated, it may be desirable to keepthis flow separate from the cleaned syngas.

The flow rate of HX cleaner gas may be separately controlled. Forexample, the flow may be continuous, or used only as needed, dependingon the deposition rate and/or total deposited amount of tars and otherparticulates. In some embodiments, the amount of particulate depositedon the filter 400 is measured and the flow rate is determined based onthis measurement. In other embodiments, a constant flow rate may beused.

During operation, the regenerator 400 is rotated in discrete steps. Itis possible to move the regenerator in such a manner that, over time,all portions of the regenerator 400 are exposed to the HX cleaner,thereby allowing for the cleaning of the entire regenerator. In someembodiments, the amount of rotation per time step may be constant. Inother embodiments, the amount of rotation is varied. This embodimentallows selective cleaning of the regenerator. Sensors may be used todetermine the loading and requirement for cleaning of a particularportion of the regenerator. The use of sensors that locally determinethe loading in the regenerator matrix may improve the operation of theregenerator by cleaning the dirtiest portions at any given time.Multiple sensor technologies may be used, including microwave sensing asdisclosed in U.S. Patent Publication 2008/0059093, optical sensing,pressure based sensing or flow based sensing, or other sensing methods.

The regenerator can be used with varying gasification rates and flowrates. There are various parameters that can be adjusted, including thespeed of rotation of the regenerator, the stationary (or dwell) time,and the ratio of the stationary time to the time of rotation. Thestationary time can be determined by calculating the dwell or residencetime of any of the multiple flows passing through the regenerator. Forexample, it may be desirable to maintain contact between the HX cleanerfluid and a section of the regenerator for a given amount of time toallow regeneration. The required stationary time can be determined basedon mass, heat, or chemical kinetics transfer rates.

Because a fraction of the heated portion 410 is placed in the thirdstream, there may be a loss of efficiency, depending on the frequency atwhich the filter needs to be cleaned. This configuration may beparticularly attractive when the enthalpy requirement of the cold streamis lower than that which can be provided by the hot stream, such asbecause of different compositions or flow rates.

As described above, in some embodiments, the raw syngas flow is not thehot stream, as the return stream may be even hotter. The use of HXcleaner fluid is also possible in this reverse configuration.

Furthermore, the present invention is not limited to one hot stream, onecold stream and one cleaner stream. For example, FIG. 5 shows aconfiguration in which there are two cold flow streams 520,540, a hotstream 510 and a cleaner stream 530. The two cold streams 520, 540 havedifferent cross sectional areas in the regenerator 500 in thisembodiment. The cross sectional areas in the regenerator 500 areselected based on the enthalpy flow requirements of each stream. Forexample, one may have a flow rate greater than the other. Alternatively,they may be comprised of fluids having a different specific heat. Inanother embodiment, the desired final temperature may be different forthe two streams 520, 540. In other embodiments, the cold streams 520,540 may have the same cross-sectional area and have identical enthalpyflow requirements. As described above, the regenerator is rotated suchthat all portions of the exchanger 500 eventually are exposed to the HXcleaner stream.

FIG. 6 shows a second embodiment with multiple cold streams 620, 640, ahot stream 610 and a cleaner stream 630. In this embodiment, the coldportions 620, 640 are created radially, rather than poloidally. Dirtysyngas passes through first portion 610 (which extends on either side ofseparator 635). The cold streams pass through portions 620, 640. Asbefore, a cleaner portion 630 (which also extends on either side ofseparator 635) is used to clean the regenerator 600, as needed. In thecenter of the regenerator 600 may be a shaft or thermal insulator 625.

Although two cold streams are shown, it is within the scope of thedisclosure to use more than two. In addition, there may be multiple hotstreams and multiple HX cleaner streams. As stated above, thetemperatures and flow rates of the cold streams do not need to be thesame. Specific enthalpy requirements can be met by selecting theappropriate cross sectional area for each stream and appropriatechoosing of the return temperatures. This may be the case in gasifiers,and particularly waste or biomass gasifiers, where there are multipleflows with multiple temperatures and throughputs.

In some applications, it would then be possible to mix the twoseparately heated streams downstream from the heat exchanger 600,thereby simplifying the plumbing requirements. It may also be possibleto provide limited turbulence in the region downstream from the heatexchanger 600 in order to improve mixing of the two cold streams,upstream from the TRC unit.

There is a pressure gradient limitation to the use of rotatingregenerators, as the seals may allow some flow across regions. Thepresent invention avoids this problem as there is not expected to besignificant pressure difference between the dirty syngas (hot stream)and the clean syngas (cold stream). The pressure of the HX cleaner fluidshould be comparable to these pressures.

It is possible to use components at the lower temperature of downstreamcomponents 220 or 221 that are not available at the higher temperature,such as pumps. Re-pressuring pumps can be placed downstream from any gascleaning components in 220.

For turbine applications, the allowable pressure differential in thedifferent streams may be as high as 4 bar. One advantage of its use as aheat transfer media for gasifiers is that there is little pressuredifferential in the multiple flows across the regenerator, therebyminimizing leakage. In addition, for gasifier applications, minorleakage is acceptable.

Another advantage of having a HX cleaner section is that by operatingthis section at a pressure slightly higher than either or both the hotor cold streams, it is possible to minimize leakage from the dirtysyngas to the clean syngas. Leakage may compromise the cleanliness ofthe syngas and could make difficult its application directly to aturbine or to a catalyst.

There are multiple techniques that can be used to add thermal energy tothe section of the energy exchanger that is undergoing regeneration.This can be achieved, as described above, by using heated cleanerfluids, by using combustion of the cleaning fluid, with the combustionoccurring either external or internal to the section of the energyexchanger that is undergoing regenerations. In other embodiments,electrical means are used to add thermal energy to the section of theenergy exchanger undergoing regeneration. In one embodiment, microwaveheating is applied to this section, with the use of microwave antennasor waveguides that are located behind a liner.

The regenerators in gasifiers can achieve multiple objectives. First, byremoving the tars from the syngas in the regenerator, the need forsubsequent syngas cleanup is reduced. The use of a separate oxidizer orHX cleaner fluid for removing the tars from the heat exchanger minimizesthe use of oxidizers in the TRC needed to remove the tars from the bulk.Furthermore, by removing the tars from the syngas and oxidizing themseparately with a different flow, it is possible to substantiallydecrease the energy required to eliminate tars. Additionally, theregenerator can be used to heat up the lower temperature flows upstreamfrom the TRC, minimizing the heat input to the TRC. The use of a ceramicheat regenerator, allows the use of the high temperatures in the rawsyngas, without the need to quench it.

The regenerator can be used in conjunction with a turbine. The turbinemay be used to compress gasses upstream, for the air-separation unit, orto generate electricity (either for internal use or for sale). It canalso be used to provide power to other rotating equipment, such asblowers.

Turbines typically need clean syngas to operate, as shown in FIG. 3A, ora separate fluid, such as helium, as shown in FIG. 3B. The regeneratorcools the dirty syngas and warms the fluid that runs through theturbine. Because of the need for seals (due to the rotational nature ofthe regenerator), there may be leakage between the hot and cold streams.In some embodiments, the pressure of the stream toward the turbine maybe as high as 4 bar. Thus, if the gasifier is operated at or nearatmospheric pressure, it is expected that turbine fluid may leak to thehot stream. In some embodiments, this leakage is acceptable, as theleaked gas simply passes through the hot stream path a second time.Thus, if the pressure in clean stream is at or above that of the dirtystream, the leakage can be assured to be from the clean stream to thedirty stream, thereby minimizing contamination of the clean stream.

Using the turbine with a gas other than syngas may have the advantagethat the requirement of the syngas may be relaxed. It may also bebeneficial to operate the turbine with a gas that has increased thermalefficiency, such as helium. However, in some embodiments, such as whenthe turbine fluid is helium, it may be necessary to recover this gasfrom the syngas. In these embodiments, it may be desirable to use aseparate heat exchanger, such as one without rotation which has noleakage.

The present approach is attractive in that the temperature of the cleansyngas may be substantially higher than what is needed for manufactureof liquid fuels (alcohols, Fisher Tropsch). It is possible to use theenthalpy of the gas for other processes, and introduce the cooled syngasinto the catalytic reactor for making liquid fuels. For example,downstream components 220 could also include catalysts, locateddownstream from the syngas cleaning unit, which is also located in thedownstream component 220, for the manufacture of liquid fuels from thesyngas. The chemical process may be endothermic, and the heat of thesyngas can be used to drive the process. Some chemical processes havethe best results (in terms of selectivity and conversion) at temperaturesubstantially colder than the temperature of the syngas as it leaves thegasifier, and the present invention allows use of the process withouthaving to waste the heat in the process. It may be possible to alsoseparate the product from the syngas by absorption, adsorption or simplyby phase change, and only return the unreacted components through theheat exchanger. It should be understood that the middle stream element221 could be used instead of the downstream component 220 for thispurpose, with a temperature higher than that of downstream component220. This arrangement is useful when the temperature required for thecleaning process of the gas is lower than the temperature needed fordriving the desired chemistry in element 221.

Desirable chemistry in downstream components 220 or 221 can also bedriven in cases when the regenerator is used to add additionaltemperature to the syngas. Already mentioned is the pyrolysis of thetars. Other desirable chemistry can take place at the highertemperature, either endothermic or exothermic.

In FIGS. 3A and 3B, it is possible that the exit temperature of the rawsyngas exiting portion 310 may still be relatively hot. In this case, itmay be possible to run a second turbine with steam. It may also bepossible to recover additional energy through the use of a second heatregenerator, as shown in FIG. 3C. Since the syngas temperatures arelower, conventional heat exchangers, such as Heat Recuperator SteamGenerators (HRSG) may be used.

Rotating regenerators require seals that allow rotational movement attimes, yet form seals when the regenerator is stationary. In addition,the present seals may be required to operate at elevated temperatures.One potential seal is a bladder that is located across the surfaces thatneed to be sealed, as shown in FIGS. 7A-B. The bladder 715 may bedepressurized, as shown in FIG. 7A. In this case, there is space betweenthe rotating element 700 and the fixed element 710, and therefore theregenerator can be rotated. Once the regenerator has been rotated thedesired amount, the bladder 715 can be pressurized, such as by puttingfluid into the bladder through port 720. This causes the bladder 715 toexpand in size, allowing it to contact the rotating element 700 and thefixed element 710, as shown in FIG. 7B. In some embodiments, the port720 is located in a colder temperature region, away from the extremeheat of the gasifier.

There are various types of seals. At lower temperatures, it may bepossible to use bladders 715 made of materials such as steel or otherconventional metals. At higher temperatures, such as above 1200° C.,refractory metals may be required. Various metals and alloys may beused. As the atmosphere may be reducing in nature, appropriate choice ofmaterial is required.

As an alternative to the use of very high temperature seals, it may bepossible to maintain the seal at a lower temperature than thesurroundings. Because there is limited heat transfer between the gas andthe bladder 715, the heat transfer is mainly due to conductive heattransfer through the elements 700, 710. Through appropriate design, itis possible to sufficiently cool the bladder to allow the use of moreconventional materials for the bladder. For example, low thermalconductivity material 730 can be added in the periphery of theregenerator, or axially to the moving element of the regenerator inorder to limit the heat transfer to the sealing region.

In another embodiment, the bladder itself can be cooled by flowingfluids or gases therethrough. FIG. 8 shows a circumferential bladder 800with two ports 810, 820. Cool fluid or gas is added in port 810, and hotfluid or gas is removed from port 820. Additional ports can be used aswell. Although a circumferential bladder is shown, this concept isequally applicable to other shapes.

Several embodiments are disclosed. Those of the art will recognize thatthe present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Further, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. A gasification system, comprising: a reactorvessel for producing raw syngas; a primary energy exchanger including afirst portion and a second portion, the first portion in fluidcommunication with the reactor vessel for receiving raw syngas from thereactor vessel, the primary energy exchanger configured to collecttherein particulates or condensables from the raw syngas, wherein theprimary heat exchanger is configured as a rotating heat regenerator; afirst flow path in fluid communication with the first portion fortransporting syngas exiting the first portion out of the primary energyexchanger; a downstream component in fluid communication with the firstflow path and configured to change a temperature of syngas received fromthe first flow path; a second flow path in fluid communication with thedownstream component for directing the syngas received from the firstflow path toward the second portion of the primary energy exchanger; anda sealing element disposed between a rotating element of the rotatingheat regenerator and a fixed element of the gasification system, whereinthe sealing element is an expandable bladder configured to be providedfrom a deflated state in which a space exists between the rotatingelement and the fixed element to an inflated state in which theexpandable bladder contacts the rotating and fixed elements.
 2. Thegasification system of claim 1, wherein the downstream component isfurther configured to remove additional particulates from the syngasexiting the first portion.
 3. The gasification system of claim 2,wherein the downstream component comprises a cooling element configuredto reduce the temperature of the syngas received from the first flowpath to allow particulates and condensables to precipitate.
 4. Thegasification system of claim 2, wherein the downstream componentcomprises a heating element configured to increase the temperature ofthe syngas received from the first flow path to allow pyrolysis ofparticulates.
 5. The gasification system of claim 2, wherein thedownstream component comprises catalysts adapted to commence chemicalreactions with the syngas received from the first flow path.
 6. Thegasification system of claim 1, further comprising a second energyexchanger, positioned in series with the primary energy exchanger. 7.The gasification system of claim 6, further comprising a middle streamcomponent located between the primary energy exchanger and the secondenergy exchanger.
 8. The gasification system of claim 7, wherein themiddle stream component is configured to introduce conditioning materialto the second flow path.
 9. The gasification system of claim 1, whereinthe primary energy exchanger includes a thermal mass.
 10. Thegasification system of claim 9, wherein the primary energy exchanger isconfigured to cause a portion of the thermal mass to be heated by syngaspassing through the first portion and cooled by syngas passing throughthe second portion.
 11. The gasification system of claim 9, wherein thethermal mass is configured to allow the particulates or condensables tobe deposited on the thermal mass, the primary energy exchanger furthercomprising a third portion configured for cleaning the thermal mass. 12.The gasification system of claim 9, wherein the thermal mass includes ahoneycomb structure, a monolith structure, or pellets.
 13. Thegasification system of claim 1, wherein the expandable bladder includesa first port for flowing a gas or fluid into or out of the expandablebladder for providing the expandable bladder into the inflated state orthe deflated state.
 14. The gasification system of claim 13, wherein theexpandable bladder further includes a second port for circulating gas orfluid through the expandable bladder for maintaining a temperature ofthe expandable bladder.